In a typical cellular radio system, also referred to as a wireless communication system, user equipments, also known as mobile terminals and/or wireless terminals communicate via a Radio Access Network (RAN) to one or more core networks. The user equipments may be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus may be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “eNB”, “eNodeB”, “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
A cellular telephone network according to the Long Term Evolution (LTE) 3GPP specifications is an example of a telecom network of today. The LTE specifications may be seen as an evolution of the current Wideband Code Division Multiple Access (WCDMA) specifications. An LTE system uses Orthogonal Frequency Division Multiplex (OFDM) as a Multiple Access Technique, called Orthogonal Frequency Division Multiple Access (OFDMA) in the Down Link (DL).
Different user equipments use the different standards such as GSM, WCDMA and LTE. With a single multi-standard base station it may be possible to support multiple accesses depending on which access-specific equipment it comprises. For example, a multi-standard radio base station may support GSM, WCDMA and LTE accesses. A necessary requirement is a power amplifier that can transmit to any access. A carrier here is meant one carrier frequency, that for example may be a 200 kHz Broadcast Channel (BCH) or Traffic Channel (TCH) for GSM, a 5 MHz wideband carrier for WCDMA or a LTE carrier of 5, 10 of 20 MHz.
This multi-access base station design opens for a change of power used by each carrier, so-called power reallocation, between accesses on the same base station. Different levels of reallocation, i.e. how often the power used by each carrier requires to be changed, may be envisioned from slow, i.e. on hour basis, e.g. by utilizing different levels of power reallocation in busy hour and in non busy hour, to fast on millisecond (ms) basis. In GSM the shortest time interval is called time-slot, and is 0.577 ms. For transmitting voice, each user equipment uses typically one time-slot to transmit the code voice bits. This time-slot is repeated every 8th time-slot, and thus 8 time-slots creates what is called a frame. In WCDMA and LTE the shortest time unit is called Transmission Time Interval (TTI). To utilize DTX variations and power allocation, the fastest power reallocation is required, i.e. per TTI and/or per timeslot, since in a time slot with DTX no power is required, since it is not possible beforehand to know when a user equipment starts to utilize DTX. Hour timescale is used to follow traffic variations such as busy hour. DTX is a method of momentarily powering-down, or muting, a user equipment or a base station when there is no voice or data input to the user equipment or to the base station. This optimizes the overall efficiency of a wireless communications system, conserves battery power and reduces interference. When reaching maximum total power within the base station, also Quality of Service (QoS) requirement differences may be utilized. The power is reallocated from the access with lowest QoS on the users, which users then will get reduced transmission power. The power is reallocated to the access with higher quality of service requirements on the users. For example: if GSM only carries voice with high QoS requirements and LTE have some users with best-effort file downloading, the power is reallocated from LTE to GSM.
FIG. 1 shows an example of a GSM time-slot (TS) and frequency structure. Time slots 0 to 7 are shown horizontal in FIG. 1. Each GSM frequency requires a transceiver (TRX), where two transceivers TRX 1 and TRX N are shown vertical in FIG. 1. In some of the time slots DTX is performed, and some time slots are free, i.e. there is no user allocated to them. In these time slots no power is required. In some time slots User Data (UD) such as e.g. data or voice is transmitted, in these time slots power is required. In this example, the high of the PC box in each time slot and transceiver represents the power used by the transceiver in this time slot. Please note that in WCDMA and LTE it is more common to refer to carrier instead of TRX.
From FIG. 1 the variations in the total GSM transmit power and corresponding time frame are shown for the transceivers, i.e. for TRX1 and TRXN altogether for each time frame. The requirement for allocation and or reallocation will follow the variations in the total GSM transmit power.
Ideally, for the best efficiency the allocation and reallocation of power between GSM and any other access should be as fast as possible. A TS in GSM is 0.577 ms which is then an ideal basis to react on for allocation and/or reallocation. For LTE the most efficient would then be to react on 1 ms basis, or alternatively to react on a GSM frame basis, around 5 ms. GSM has a power plan 8 TSs ahead, i.e. in GSM power is planned 8 TSs ahead, and therefore it is possible to know beforehand which of the 8 TSs that has the highest total transmit power over all TRX:s, and use this for a limit of the shared power and share the rest up to maximum of all GSM TRX:s, see FIG. 2.
FIG. 2 depicts a schematic scheme of fast power sharing between GSM and LTE. The vertical axis represents power and the horizontal axis represents time slots. The lower part of FIG. 2 represents GSM with two transceivers TRX #1 and TRX #2. In FIG. 2 boxes are depicted. Each box has a number representing transmit power of a user equipment numbered with that number. Boxes 1, 3, 5, 7, 9, 11, 13 and 15 in GSM time slots in the first GSM frame, and boxes 1 and 3 in GSM time slots in the next GSM frame, represents transmit power used for that respective time slot by TRX #1. Boxes 2, 6, 8, 10, 12, 14, and 16, in the GSM time slots in the first GSM frame, and box 2 in a GSM time slot in the next GSM frame represents transmit power used for that time slot by TRX #2. The upper part of FIG. 2 represents LTE and shows five LTE time slots. Each LTE time slot is represented by a box wherein the height of each box represent the maximum power used in this time slot since in this example it is assumed that the LTE always tries to transmit with maximum, serving very high bit-rate demanding services such as downloading a file, with no upper limit of the maximum bit rate, i.e. Pmax LTE-static.
In order to avoid sharing every GSM time slot of 0.577 ms, the maximum total power during a GSM frame, i.e. Pmax GSM-power-used-during-a-frame is used as the “limit” for power sharing. The rest of the power, i.e. the power from Pmax GSM-power-used-during-a-frame up to Pmax GSM-static, may be shared by LTE or WCDMA. Where Pmax GSM-static is the total power that is allocated for GSM.
However, the power sharing may be a rather slow process e.g. in the order of 10-20 s. There may be several reasons for this. First, it may be the hard-ware that limits the process speed. Also, it may be beneficial to do the power sharing or power reallocation rather seldom in order to not jeopardize the system stability due to e.g. too fast changes in transmit power. To share all GSM excess power to LTE/WCDMA may therefore lead to bad QoS for the GSM system since an existing GSM speech service may suddenly need the shared power, or a new GSM user arrives suddenly to the system and requires transmit power.
Relating to FIG. 2, assume for example that GSM shares all available power with LTE, where the maximum total power i.e. Pmax GSM-power-used-during-a-frame during a GSM frame is used as the “limit” for power sharing. The rest of the power, may be shared by LTE or WCDMA, i.e. the power from Pmax GSM-power-used-during-a-frame up to Pmax GSM-static. This assumes that the power scheme may be altered every GSM frame. If that is not the case, a new GSM user may arrive which requires more total transmit power for that time slot than is available for GSM at the moment, i.e. the second time slot FIG. 2. This user must most probably be blocked. I.e. a problem with power sharing is that if the power sharing is relatively slow, e.g. slower than ˜5-10 ms, it is not possible to share all unused GSM power to LTE and still maintain the GSM QoS.